This is a continuation of application Ser. No. 07/847,301, filed Mar. 6, 1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a planar antenna in general and, more specifically, to a planar antenna with a directional pattern adjustable by means of an adjustment feed by way of a passive network.

2. Description of the Background Art

Microstrip beam antennas are well known in the art and present a number of disadvantages, e.g. narrow bandwidth and low efficiency, in addition to their essential advantages which result from desirable dimensions, simplicity of manufacture, and compatibility with printed circuits. In many respects, the manufacturing technology employed in microstrip antennas has not met established environmental specifications, which has resulted in these antennas being used only to a limited extent.

EP-A-O 253,128 describes a planar suspended conductor antenna array comprising tiered substrates between a pair of conducting plates. Each plate has openings spaced at intervals that define radiation elements. At least one exciter probe on a substrate has a plurality of openings. The signals received with these exciter probes are input to a suspended conductor in phase by means of conducting films. Holders for the substrate are mounted around the openings. The substrate is accordingly evenly supported and cannot warp. There are a number of wide grooves in the printed circuit boards between each row of adjacent openings, in which a plurality of suspended conductors are tip-stretched parallel to each other.

Antennas of this type are provided for high-frequency satellite transmissions. Because of the simplicity of the design, manufacturing costs can be lowered while high performance characteristics are achieved.

With an antenna having the above-described structure, the radiation pattern is exclusively in the form of a beam, such as is known, for example, from radar engineering.

A similar method is discussed in an article in Electromagnetics, Vol. 9, 1989, pages 385-393. This article describes a further development which is an antenna designed as a strip-slot-foam-inverted patch (SSFIP) antenna.

This SSFIP antenna is formed having tiered layer structure. Specifically, the SSFIP comprises a microstrip (S strip) with a quarter-wave stub, a slotted base, a foam layer characterized by slight attenuation and low relative permittivity, and lastly, an inverted radiating element in the form of a patch printed on a cover (inverted patch). One advantage of an antenna of this type is represented by simplicity in achieving circular polarization, and the possibility of operating two polarizations simultaneously.

In this design, the foam layer prevents surface wave propagation and increases the bandwidth.

There are several problems associated with the known SSFIP antennas described above. For example, there is a need for these antennas to be assembled with simpler and less expensive materials. Also, these known antennas have not been amenable to tailoring the radiation to specific needs.

The present invention is directed to overcoming the problems associated with the prior art antennas as will become apparent from the features described and claimed as follows.

SUMMARY OF THE INVENTION

In accordance with the present invention, a planar antenna is disclosed comprising a substrate having applied thereto electrically conductive elements, or patches, and a metal layer having a slot pattern wherein the slots and patches are aligned, as well as a base substrate. Also, supported between the metal layer and base substrate is a strip conductor network wherein a first foam material layer is formed between the network and metal layer and a second layer of foamed material is formed between the conductor network and the base substrate. The external surface of the antenna consists of glass and can be easily cleaned. The planar antenna according to the present invention can be manufactured inexpensively and enables propagation patterns to be easily shaped as desired.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with one embodiment of the invention, FIG. 1 illustrates a planar antenna which comprises four elements: a carrier plate 1, a metal layer 2, strip conductor feeding network 22 and a ground plane 3. The carrier plate 1 is preferably made of glass or a fiber composite, on which radiation elements 11 may be vacuum deposited or applied by a printing process as inverted radiating antenna elements. Planar radiation elements 11 of this kind are also called patches.

In the state-of-the-art arrangement described in the above-referenced article in Electromagnetics, Volume 9, 1989, pages 385-393, there is a foam insert behind these inverted radiation patches. It has been found, however, that surface wave propagation does not occur to the extent expected, which enables this layer to be omitted. If this layer is omitted, the following slot radiating layer can be positioned closer to the plane of the inverted radiating patches.

In contrast, the present claimed invention provides a foam dielectric layer 23 between the metal layer 2 with radiation openings 21 and strip conductor network 22 on one side, and a foam layer 24 between the latter and the ground plane 3. Ground plane 3 consists of metal or of a layer of metal deposited on a base. In addition, polystyrene, polypropylene, or polyamide are suitable as foamed materials.

In any event, the foam layer must possess both low density and a low relative permittivity.

In a preferred embodiment, the two foam layers 23 and 24 are not of equal thickness. Also according to a preferred embodiment, the thinner of the two, layer 23, is mounted on the coupling side and the thicker, layer 24, is mounted between the strip conductor network 22 and the ground plane 3.

As shown in FIG. 1, one side of the carrier plate 1 seals off the environment. On its inner surface, the carrier plate has electrically conductive patches 11, which, as is to be seen from FIG. 2, may be square in shape, for example, and be spaced at regular intervals from each other. These electrically conductive patches can be any suitable material, such as a suitable conductive metal, and may be applied in any suitable manner, such as being vapor deposited, laminated, or printed. Opposite each patch 11 is a coupling network consisting of slot-like openings (coupling slots) in the metal layer 2, as shown by FIG. 8. Layer 2 rests on the foam layer 23. On the reverse side of layer 23 is located a distribution network 22, as shown in FIG. 9, by means of which the transmittivity of the coupling slot 21 are controlled. The leads required for this purpose are on the reverse side of the foamed material 23. The ground plane 3 provides a seal from the environment. It consists of metal or is designed as a metallic reflector.

In accordance with further aspects of the invention, three additional modifications of the SSFIP technology are utilized which, for the most part, contribute the bandwidth enlargement or reduction of the reflection factor.

First, the openings 21 in the radiation plate 2 can be H-shaped and butterfly-shaped, as illustrated by the configuration in FIG. 3, in addition to being in the form of slots.

Second, the stub cables (under the openings 21) in the distribution network 22 are impedance matched. Two forms of such fully matched strip conductor networks are shown in FIG. 4.

Also, the radiation elements (patches 11) may be square, round, rectangular, or cross-shaped or may have a series of strips of equal or unequal length and varying width. A typical patch in strip form is shown in FIG. 5. The length of the various segments 111 of a patch is adjusted in such a way that the frequency band of each segment overlaps a part of the overall desired frequency spectrum (and consequently each coupling slot is tuned to the particular frequency associated with each patch).

In contrast to the above-referenced Electromagnetics publication, the antenna of the present invention is constructed having substrates no longer consisting of Teflon materials. Carrier plate 1, for example, consists of easily disposable glass. Glass as a seal against the environment presents a great advantage in that it can withstand all harmful environmental influences and can easily be cleaned when necessary. In addition, an antenna of this design could be easily and simply integrated into the facades of high-rise buildings. The coupling network is mounted between foamed material and air, and in this instance, is held in position relative to Carrier plate 1 by spacers.

The antenna may be assembled with one or more elements (patches). Several elements may be arranged either in a column or side by side.

The customary vertical radiation pattern as illustrated in FIG. 6 exhibits distinct zero settings 41 between the individual beams 40, 42. Controlling the coupling slots 21 by means of the distribution network 22 allows uniform illumination of the area to be irradiated. In the examples discussed in the foregoing, it has been customary with the state-of-the-art equipment for the direction of maximum radiation to be positioned perpendicular to the plane of the antenna, so that this antenna plane has had to be mounted obliquely for illumination, as shown in FIG. 6.

The antenna design of the present invention now makes it possible to orient the direction of maximum radiation in a limited range, from the electrical viewpoint at any rate, so that the plane of the antenna can be mounted independently of the direction of maximum radiation, as is clearly seen from FIG. 7. In addition to the suitably shaped major lobe 44 as shown in FIG. 7, a side lobe 45, for example, can be directed and amplified in such a way that an area so remote as not to be irradiated by the major lobe 44 can be illuminated. In addition to generation of an optimized vertical radiation pattern, generation of the horizontal beam direction at any desired angle of approximately .+-.30.degree. to the vertical of the plane of the antenna is possible. Similarly, more than one arbitrary direction of radiation is also possible in the horizontal plane.

In the past, it has been possible to build antennas measuring up to about only 30 cm by 30 cm as a result of constraints imposed by costs, technology, and the manufacturing process. According to the present invention, antennas can be built which are suitable for reception by way of satellites for music broadcasting, flat antennas 3 to 4 cm thick and of almost any desired size. The only constraints imposed are represented firstly by the glass area that can be obtained, and secondly, by the area that can be printed by screen printing.

In the example shorn in FIG. 2, the patches are drawn as squares. It is obvious to any expert, however, that other geometric shapes are possible as patches, as for example circular areas, ellipses or rectangles, or parallel strips.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described as follows with reference to the drawings, in which:

FIG. 1 illustrates a cross-section view of an antenna according to one embodiment of the present invention;

FIG. 2 illustrates a top view of a patch pattern on the antenna according to the present invention;

FIG. 3a is a schematic representation of a butterfly shaped coupling slot;

FIG. 3b is a schematic representation of a coupling slot shaped in the form of the letter H;

FIG. 4 illustrates impedance matching of the conducting strip networks to the coupling slots in accordance with the present invention;

FIG. 5 shows a typical form of a slotted patch adapted for wideband operation;

FIG. 6 illustrates a vertical propagation pattern with unadjusted re-radiation;

FIG. 7 shows a vertical propagation pattern wherein the re-radiation is adjusted;

FIG. 8 is a top view of a coating of a coupling network with slotted openings according to one embodiment of the present invention; and

FIG. 9 is a top view of coating of a distributed network according to one embodiment of the present invention.